The process of using ion-exchange resins for removing electrolyte from an electrolyte solution is generally used because of the reason of convenience for handling. (H. Sato, Membrane 7, 156 (1982)) Further, the desalination process by electrodialysis using ion-exchange membranes is also known. This desalination process is as follows:
A compartment for dealing with water is provided by an arrangement of cation-exchange membranes and anion-exchange membranes. Then, an electrolyte is divided between a first compartment having high ion concentration and a second compartment having low ion concentration by means of providing the water to the compartment and of applying electric field of direct current perpendicular to the membrane. Then, the desalinated water is obtained by means of collecting the water from the second compartment. The desalination process is characterized by high rejection.
The process using ion-exchange resins, however, has the problem that the intermittent regeneration is necessary and that the continuous operation is difficult to carry out.
On the other hand, the desalination process by electrodialysis using ion-exchange membranes also has the problem that gas is produced on electrode, and that the efficiency of desalination decreases due to the decrease of electric current density when the water having low ion concentration is dealt with.